1. Field of the Invention
The present invention relates to a method of accessing a disc-shaped recording medium for use with an optical disc drive or the like, for example.
2. Description of the Prior Art
Disc drives have hitherto been proposed to record data on an optical disc, such as a magnetooptical disc and a write-once optical disc, and to reproduce recorded data from the optical disc. Disc drives are now widely used as devices for storing computer data and audio-visual data.
As a format of such optical disc, there is known a so-called zone constant angular velocity (CAV) system which records and/or reproduces data on and/or from an optical disc at clock rates different in each zone in a plurality of zones divided along the radius direction of the optical disc by rotating the optical disc at the CAV. The same assignee of the present application has previously proposed this zone CAV system (see Japanese laid-open patent publication No. 5-54540).
Optical disc media used in the zone CAV system are not satisfactory in error rate as compared with magnetic discs. To solve this problem, the optical disc employs an error correction code (ECC) which is more powerful than that used in the magnetic disc and two processing algorithms are proposed for defect sectors. One processing algorithm is what might be called a sector slipping algorithm (SSA) and another is what might be called linear replacement algorithm (LRA).
The SSA designates the sector of a defect sector as a replacement sector and uses the replacement sector instead of the defect sector when optical discs are initialized upon manufacturing. Accordingly, when data is written in and/or read out from the data block, a data transfer rate is not decreased substantially. If the replacement sector is not accessed upon first access, the replacement sector can be accessed when the optical disc is rotated once. SSA information, i.e., information representing the original sector of the sector of the replacement sector is generated when the optical disc is initialized in the manufacturing process and recorded on a predetermined position of the optical disc.
According to the LRA, when data is written in the optical disc in actual practice, written data is read out from the optical disc. It is verified whether or not the read-out data and the written data with each other. Then, a replacement sector of a defect sector is designated on a track determined as a replacement sector area. LRA information, i.e., information representing the original sector of the sector of the replacement sector, is recorded on the optical disc not only when data is written on the optical disc but also when the optical disc is initialized in use.
The SSA information and the LRA information are recorded on predetermined areas of the optical disc. Specifically, disc definition structure (DDS) information, primary defect list (PDL) information and secondary defect list (SDL) information are recorded on predetermined areas of the optical disc. The DDS information is data showing data structure of the optical disc and includes PDL start address data and SDL start address data. The PDL information is data concerning sectors which are replaced according to the SSA. The SDL information is data concerning sectors which are replaced according to the IRA. The DDS information, the SSA information and the LRA information will be collectively referred to hereinafter as "defect information".
The defect information is recorded on the optical disc totally in four positions. Two of the positions are near the outermost periphery and two of the positions are near the innermost periphery in order to detect a new defect sector when the optical disc is initialized in the manufacturing process or when the optical disc is initialized after the optical disc has been manufactured.
If it is determined by simultaneous verification that sectors of the above-mentioned four positions are all defect sectors when the defect information is recorded on the optical disc, then such an optical disc is determined to be a defect optical disc.
An example of the format of the conventional optical disc will be described with reference to FIGS. 1 to 4.
FIG. 1 of the accompanying drawings, shows a physical track Ta1 of the starting portion, where information DDS#0 is recorded on a physical sector 0, information PDL#0 is recorded on a physical sector 1, and information SDL#0 is recorded on a physical sector 2 of a physical track 0, respectively. Information DDS#1 is recorded on a physical sector 12, information PDL#1 is recorded on a physical sector 13, and information SDL#1 is recorded on a physical sector 14 of a physical track 1, respectively.
Physical track Ta2 of the ending portion, is also shown wherein information DDS#2 is recorded on a physical sector 0, information PDL#2 is recorded on a physical sector 1, and information SDL#2 is recorded on a physical sector 2 of a physical track 9998, respectively. Information DDS#3 is recorded on a physical sector 12, information PDL#3 is recorded on a physical sector 13, and information SDL#3 is recorded on a physical sector 14 of a physical track 9999.
Tracks and sectors that are respectively referred to as "physical tracks" and "physical sectors" represent physical positions of tracks and sectors on the optical disc directly. DDS#1 to DDS#3 are informations representing the same thing but DDS#1 to DDS#3 are different in value because DDS#0 to DDS#3 also contain information representing recorded positions of the corresponding PDL#0 to PDL#3 and SDL#0 to SDL#3. In other words, information PDL#0 and information PDL#1 are recorded on the optical disc at different positions.
This is also true in the information PDL and the information SDL. The defect information is recorded on the optical disc at the four positions described above. The reason for this is that, if information that was recorded only on one position of the optical disc was not read out therefrom, the optical disc would become useless.
FIG. 2 is a schematic diagram used to explain an example of the format of the information PDL. As shown in FIG. 2, the information PDL is a table composed of physical track Nos. (3 bytes) and physical sector Nos. (1 byte) provided at every defect #1 to #n in response to the defects #1 to #n. The physical track Nos. depict the physical track Nos. of the defects #1 to #n, and the physical sector Nos. depict the physical sector Nos. of the defects #1 to #n.
FIG. 3 is a schematic diagram used to explain an example of the format of the information SDL. As shown in FIG. 3, the information SDL is a table composed of physical track Nos. (3 bytes) and physical sector Nos. (1 byte) provided at every defect #1 to #3 in response to the defects #1 to #n, physical track Nos. (3 bytes) and physical sector Nos. (1 byte) of replacement sectors provided at every defect #1 to #3.
Operation of the conventional optical disc drive will be described below with reference to the flowchart in FIG. 4.
Referring to FIG. 4, following the start of operation, a host computer outputs a logical address at step S1. The optical disc drive reads out defect information recorded on the optical disc when the optical disc is loaded thereto or when the optical disc drive is energized and generates a conversion table. Then, the processing proceeds to step S2.
In step S2, a physical address is calculated from address data based on the conversion table. A central processing unit (CPU) calculates a physical address of the optical disc based on the logical address supplied thereto from the host computer and the conversion table. The conversion table is used to directly convert the logical address supplied from the host computer to physical address. Then, the processing proceeds to step S3.
In step S3, the physical address is supplied to the optical disc drive and then, the processing routine is ended. The CPU supplies the physical address obtained at step S2 to a servo controller. The servo controller moves a pickup device by energizing a driver unit based on the physical address supplied thereto from the CPU and energizes the pickup device to start reading and/or writing. When the pickup device reads out digital data from the optical disc, data obtained by the pickup device is supplied to the host computer.
A wide variety of patent applications concerning the zone CAV system have been made but they have not yet been put into practice.
When an optical disc apparatus of zone CAV system is realized, defect sectors should be handled similarly to the prior art. Specifically, the address requested by the host computer has to be converted to an address on the disc surface of the optical disc, i.e., a physical address which considers the number of sectors of one track which changes at every defect sector and zone.
Therefore, if the address requested by the host computer is directly converted into the physical address similarly to the prior art, then calculation becomes very complicated.
As a result, programming for the host computer becomes enormous and a processor with high throughput is required to process such enormous programming. Further, if a processor with low throughput is used, then it takes a lot of processing time.
If data to be handled is data such as audio-visual data that requires a medium of large capacity, then it is suggested that the capacity of the optical disc be increased without increasing the diameter of the optical disc. However, at present, even though the capacity of the optical disc can be increased, such optical discs cannot be made compatible with the existing optical disc drive and an optical disc drive that is exclusively-designed for such optical disc should be developed.
When the CAV system is adopted and defect information is recorded totally in four positions, two of which are on the outermost periphery and two on the, innermost periphery of the optical disc, there is then the large possibility that the innermost peripheral portion of the optical disc will be damaged so that defect information recorded on the portion near the outermost peripheral portion of the optical disc cannot be read out. Further, recording density is increased in the innermost peripheral portion of the optical disc so that yield in the portion near the innermost peripheral portion is poor. There is then the large possibility that defect information recorded on the portion near the innermost peripheral portion of the optical disc cannot be read out. Specifically, there is then the very large probability that the optical disc will become a defect disc.
Moreover, it is customary that optical discs that become defect discs are discarded. This is not preferable from a natural resources saving standpoint.